2017 vs 2018 BMW 4 Series

Both years

• Water trapped in the convertible's rear side panels All years

  What to check: Listen for water sloshing in the rear side panels while driving, run each rear window and the roof, and look for water or a musty smell in the corners of the trunk. Ask whether the drains have been cleared.

  BMW of North America's bulletin says the rocker trim and underbody panel can sit too tight against the drain plugs, so water fills the lower rear side panels and can corrode the rear window regulators and motors, then reach the trunk's audio amplifier. It extends coverage of the drain repair to 15 years or 150,000 miles from first delivery. On a British owners' forum, owners of four convertibles in three threads report a rear window or the roof stopping working from water in the panel, and another found water running out of a sill after a car wash.

  BMW, owners' reports (unofficial)

• Coolant leaks on the B48 four 2017–2020 One source so far

  What to check: Look for coolant at the upper radiator hose and the oil filter housing.

  Euro Premium Parts reports occasional leaks at these two points.

  A seller's guide (unofficial)

Both years

Engines

2.0L turbo four-cylinder (2017–2020) Edmunds, a published reference, 3.0L turbo inline-six (2017–2020) Edmunds, a published reference

Transmissions

Eight-speed automatic Edmunds, CarGurus, Six-speed manual Edmunds, CarGurus

Drivetrains

Rear-wheel drive Edmunds, a published reference, xDrive all-wheel drive Edmunds, CarGurus

Body styles

Coupe Edmunds, a published reference, Convertible Edmunds, CarGurus, a published reference, Gran Coupe (2015–2020) Edmunds, a published reference

Packages

Luxury Line, later Luxury Package Edmunds, a published reference, M Sport Edmunds, a published reference, Premium Package Edmunds, Technology Package Edmunds, Lighting Package Edmunds, Cold Weather Package Edmunds, Driver Assistance Package Edmunds, Driver Assistance Plus Package Edmunds

Both years

• Alpine White 2015–2019 Edmunds
• Estoril Blue 2015–2019 Edmunds
• Imperial Blue Metallic 2015–2019 Edmunds
• Black Sapphire Metallic 2015–2019 Edmunds
• Glacier Silver Metallic 2015–2019 Edmunds
• Jet Black 2015–2019 Edmunds
• Melbourne Red Metallic 2015–2019 Edmunds
• Mineral Grey Metallic 2015–2019 Edmunds
• Mineral White Metallic 2015–2019 Edmunds
• Sparkling Brown Metallic 2015–2019 Edmunds

Both years

• Venetian Beige Dakota 2015–2019 Edmunds
• Black SensaTec 2015–2019 Edmunds
• Venetian Beige SensaTec 2015–2019 Edmunds
• Black Dakota with Red Highlight 2015–2019 Edmunds

Both years

• Sought after: The six-cylinder 440i 2017–2020 One source so far

  Euro Premium Parts calls the B58 six the most reliable petrol choice in this generation and highly recommends it. A seller's guide (unofficial)